For any positive integer $k$, the following equation holds:
$1+2+3+\cdots+k=\frac{k(k+1)}{2} .$ Use this fact to prove that for all $k>100$, the value of the sum of the first $k$ integers is greater than 5000 . What does this have to do with the limit of a sequence of sums as $k \rightarrow \infty$ ?